Lesson Plan - Get It!
Is it possible to break or crack this rock without touching it?
Rock, minerals, and soil are not stationary or unchanging objects.
While they are incapable of moving or changing themselves, they are frequently moved and changed by people and natural forces. The process of breaking down and moving rock, mineral, and soil is called weathering, erosion, and deposition.
In this lesson, you will learn about weathering.
Weathering is the process of breaking down, or changing, rock, minerals, and soil. There are three types of weathering: physical, chemical, and biological.
Physical weathering is also referred to as mechanical weathering. Physical weathering occurs when large rocks or sections of soil break off into smaller pieces called sediments.
There are two processes that can cause physical weathering:
- First, when there are droughts, or long periods of time without rain, rocks and soil can dry out and crack. During rainy seasons, water can become trapped inside the cracks in rocks and soil. If this water freezes, the frozen water, or ice, expands, and as it does, it causes the rock or soil to break. To examine pictures of physical weathering, visit © The Geological Society of London's web page, Physical Weathering.
- Another type of weathering is chemical weathering. Chemical weathering affects the atomic makeup of the rock or soil. Acid rain is acidic precipitation that is created by pollution in the atmosphere. Acidic material contains a lot of hydrogen ions. These excess hydrogen ions can cause chemical reactions, such as burns, rust, and corrosion. Lemons and limes are both acidic. This is why they taste sour. Acid rain can cause a chemical reaction to occur in rocks and soil, changing them into something else. (If you are unsure what is meant by atomic structure, review the Elephango lesson found in the right-hand sidebar under Additional Resources.) To learn about other types of chemical weathering, check out © The Geological Society of London's Chemical Weathering page.
- The final type of weathering is called biological weathering. Biological weathering has to do with the effects of plants and animals on rocks, minerals, and soil. As plants grow, their roots can move materials in the Earth, breaking apart rocks and soil. Fungi and algae can grow on rocks, causing them to break down. © The Geological Society of London's page, Biological Weathering, has some excellent pictures of rocks that have been affected by biological weathering.
Now that you know what weathering is and the different types of weathering, move on to the Got It? section to assess what you have learned.